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    <title>Document</title>
    <script>
    //1.新增数组元素，修改length长度
     var  arr =['white','yellow','black'];
     console.log(arr.length); 
     arr.length=5;//把数组长度修改为5
     console.log(arr);
     console.log(arr[3]);
     console.log(arr[4]);
     //2.新增数组元素 修改索引号 追加数组元素
     var  arr =['white','yellow','black'];
     arr1[3] ='pink';
     console.log(arr1);
     arr1[4] ='hotpink';
     console.log(arr1);
     arr1[0]='yellow';//替换原来的数组元素
     console.log(arr1);
     arr1='大脑饱和了'
     console.log(arr1);//不能直接狗日数组名赋值，否则里面的数组元素都没有了=【'、[p[\1  q   qwA  ]
    </script>
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